1. Technical Field
The present invention relates to a method for manufacturing a semiconductor device, and in particular relates to a method for manufacturing a semiconductor device having a high breakdown voltage transistor and a low breakdown voltage transistor both provided on a same semiconductor substrate.
2. Related Art
FIG. 8A is a sectional view showing an example of a method for manufacturing a semiconductor device having a high breakdown voltage transistor (hereinafter referred to as an “HV transistor”) 110 and a low breakdown voltage transistor (hereinafter referred to as an “LV transistor”) 120 provided on a same silicon substrate 101. On the silicon substrate 101 are formed a thick field oxide film 111 and a thin field oxide film 121.
Next, a gate electrode 113 of the HV transistor 110 is formed so as to be extended from a top surface of a gate oxide film 112 onto a top surface of the thick field oxide film 111, and a gate electrode 123 of the LV transistor 120 is formed from a top surface of a gate oxide film 122 onto a surface of the thin field oxide film 121. Then, after forming a source/drain region and the like of each of the HV transistor 110 and the LV transistor 120, an interlayer insulation film 130 is formed on an entire surface of the silicon substrate 101 to cover both transistors.
Next, using photolithography and dry etching, the interlayer insulation film 130 is partially dry-etched to form a contact hole 131 on the gate electrode 113 extended onto the field oxide film 111 and to form a contact hole 133 on the gate electrode 123 extended onto the field oxide film 121. Additionally, a contact hole 132 is formed to directly contact with the silicon substrate 101. Thereafter, for example, a metal layer made of aluminum or the like is embedded into each of the contact holes 131 to 133 to form a contact electrode (not shown).
In the semiconductor device shown in FIG. 8A, a top surface of the gate electrode 113 extended onto the field oxide film 111 is in a position higher than a top surface of the gate electrode 123 extended onto the field oxide film 121 when sectionally viewed. Thus, when forming the contact holes, the contact hole 131 is opened (completed) faster than the contact hole 133. During a time until the contact hole 133 is opened, the surface of the gate electrode 113 is exposed to an etching atmosphere at a bottom of the contact hole 131. For example, when forming the contact holes by plasma etching, the surface of the gate electrode 113 is exposed to a plasma atmosphere, so that plasma charge is applied to the gate oxide film 112 via the gate electrode 113. Consequently, the plasma charge can cause damage to the gate insulation film (the gate oxide film 112), which can lead to destruction of the gate insulation film.
In order to prevent the insulation destruction, JP-A-1994-310713 discloses a method as shown in FIG. 8B, for example. In the drawing, a fuse 114 is formed so as to be continued to the gate electrode 113 of the HV transistor such that the gate electrode 113 is electrically in contact with another active area other than the gate oxide film 112. The gate electrode 113 and the fuse 114 are simultaneously formed, for example, by the deposition and patterning of a polysilicon film. Thereafter, the interlayer insulation film 130 is formed, which is followed by the formation of the contact holes 131 to 133. In the method, plasma charge is applied to the silicon substrate 101 from the gate electrode 113 via the fuse 114, so that there is no damage to the gate oxide film 112 due to the plasma charge.
In the above method disclosed, however, after the formation of the contact holes 131 to 133, cutting of the fuse 114 is needed, for example, at positions indicated by broken lines shown in FIG. 8B to disconnect the gate electrode 113 from the active area. This increases the number of processing steps for photolithography and dry etching. Additionally, when cutting the fuse 114, the plasma charge may be applied to the gate oxide film 112 via the gate electrode 113, thereby causing damage to the gate oxide film 112.